The specific aims of this project are 1) To describe the pathology of minor head injury in terms of the distribution and severity and axonal and neuronal disruption. 2) To determine the threshold for pathological change expressed in clinical, neurological and biomechanical terms. 3) To correlate the pathology with the clinical findings, and 4) To determine the reversibility of pathological change. 5) To confirm the degeneration at the electron microscopic level, and 6) To determine how quantitatively reproducible the degeneration is at the electron microscopic level in terms of the extent of terminal degeneration induced by a given insult. This latter evaluation will be important in setting the stage for an evaluation of whether sprouting occurs in response to the injury resulting in the replacement of degenerating elements. The methodology to be employed will be a series of silver impregnation techniques all of which are basically modifications of the original Nauta-Gygax method. Fink-Heimer and De Olmos's cupric silver methods will be used. The experimental model utilizes the Philadelphia acceleration technique in which clinical outcome can be predicted in terms of biomechanical events. This allows various clinical grandes of head injury to be reproducibly achieved. The electron microscopic methods will involve quantitative studies of the numbers of degenerating and normal synapses after a given injury. While we are very interested in a description of the pathological events with minor injury, we also plan to determine the time course of disappearance of degeneration and, ultimately, we will be interested in possible mechanisms of recovery.